JP2017036491A - Non-oriented electrical steel sheet excellent in iron loss and manufacturing method thereof - Google Patents

Abstract

A non-oriented electrical steel sheet having excellent magnetic properties is provided. SOLUTION: C, Si, Mn, Al, P, N are contained in a predetermined range, S: 0.0010 to 0.05%, Cu: 0.01 to 3.00% are contained, and V : 0.002 to 0.20%, Nb: 0.002 to 0.20%, Ti: 0.002 to 0.10% of one type or two or more types, with the balance consisting of Fe and impurities, Diffraction intensity I2θ = 46.8 appearing at 2θ = 46.8 °, diffraction intensity I2θ = 34.4 appearing at 2θ = 34.4 °, and 2θ = 43.3 obtained by X-ray diffraction with respect to the electrolytic extraction residue A non-oriented electrical steel sheet excellent in iron loss satisfying the following formula 1 is adopted in which the diffraction intensity I2θ = 43.3 appearing at ° and the diffraction intensity I2θ = 51.6 appearing at 2θ = 51.6 °. 0.1 ≦ I2θ = 46.8 / (I2θ = 34.4 + I2θ = 43.3 + I2θ = 51.6) Equation 1 [Selection] None

Description

  The present invention relates to a non-oriented electrical steel sheet excellent in iron loss and a method for producing the same, and more particularly to a non-oriented electrical steel sheet excellent in iron loss used as an iron core material for electrical equipment and a method for producing the same.

  Non-oriented electrical steel sheets are used as iron core materials for various motors for heavy electrical equipment and home appliances. Non-oriented electrical steel sheets are commercially graded by iron loss, and are used properly according to the design characteristics of the motor and transformer.

  In recent years, further reduction in iron loss has been strongly demanded for non-oriented electrical steel sheets from the viewpoint of energy saving. In general, when fine precipitates are present in a steel sheet, domain wall movement is hindered and hysteresis loss is deteriorated.

  Therefore, conventionally, for the purpose of improving the iron loss of non-oriented electrical steel sheets, the precipitation control of sulfide in hot rolling, the reduction method of sulfide by desulfurization, the suppression of precipitation of Cu sulfide by rapid cooling after finish annealing, etc. A method has been proposed.

  For example, in Patent Document 1, a steel slab containing 0.2% or less of Cu is held for 30 minutes or more in the range of 900 to 1100 ° C., then held at a high temperature at 1150 ° C., and subsequently rolling is started and finished. Disclosed is a method for controlling the dispersion state of Cu sulfide to be favorable for the magnetic properties of the non-oriented electrical steel sheet, that is, the iron loss and the magnetic flux density, by suppressing the cooling rate during hot rolling to 50 ° C./second or less. ing.

  In Patent Document 2, CaSi is added to molten steel by the completion of casting, the S content is controlled to 0.005% or less, the slab is heated at a temperature of 1000 ° C. or higher, and then hot-rolled to a specific temperature. Disclosed is a method for avoiding the formation of fine precipitates by coiling in the zone.

  Patent Document 3 discloses a technique for suppressing the precipitation of Cu sulfide by quenching at a cooling rate of 10 to 50 ° C./sec between a temperature range of 500 to 600 ° C. and 300 ° C. after finish annealing. ing.

  Patent Documents 4 to 7 disclose technologies that expect an improvement in magnetic properties by controlling the cooling rate after finish annealing.

JP 2010-174376 A Japanese Patent Laid-Open No. 10-183244 JP 09-302414 A JP 2011-006721 A JP 2006-144036 A JP 2003-113451 A International Publication No. 2014/168136

CAMP-ISIJ Vol. 25 (2012), p1080 CAMP-ISIJ Vol. 22 (2009), p1284 j. Flux Growth vol. 5 (2010), p48 Tetsu-to-Hagane vol. 100 (2014), p1229 Tetsu-to-Hagane vol. 83 (1997), p479 Tetsu-to-Hagane vol. 92 (2006), p609 Bunnseki vol. 11 (2002), p639

However, the conventional methods described in Patent Documents 1 to 6 have the following problems.
The method described in Patent Document 1 has a problem in productivity, such as an increase in rolling load due to a lower slab heating temperature and difficulty in strict control of the cooling rate.

  Further, in the method described in Patent Document 2, high-purity steel is essential, but formation of fine Cu sulfide by Cu mixed at an unavoidable level is unavoidable, so that there is a problem that magnetic properties are deteriorated due to Cu mixing. there were.

  Patent Document 3 discloses a method of quenching from 500 to 600 ° C. to 300 ° C. at a cooling rate of 10 to 50 ° C./second, but Cu sulfide is 50 ° C./second or more. It is known from Non-Patent Documents 1 and 2 that precipitation occurs during cooling even at a cooling rate of 5%. That is, it is difficult to completely suppress the precipitation of Cu sulfide by the technique of Patent Document 3 that performs cooling at about 10 to 50 ° C./second.

  Further, in Patent Documents 4 to 6, it is possible to avoid the introduction of cooling strain into the steel sheet by the above-described method and reduce iron loss deterioration, but it is impossible to control the precipitation state of Cu sulfide. The finely precipitated Cu sulfide adversely affects the magnetic properties.

  Patent Document 7 discloses a technique for controlling the precipitation form of Cu sulfide. However, when a precipitate other than Cu sulfide (such as nitride) exists, detoxification of Cu sulfide is difficult. There was a problem of becoming.

  In view of the above-mentioned problems, the present invention provides a non-oriented electrical steel sheet excellent in iron loss and a method for producing the same, without controlling the precipitation form of Cu sulfide and causing an increase in cost or a decrease in productivity. For the purpose.

  In order to solve the above problems, the present invention has repeatedly investigated the influence of steel plate components and production conditions on the relationship between the state of sulfide dispersion and the magnetic properties. As a result, a non-oriented electrical steel sheet containing at least one of vanadium nitride (hereinafter referred to as VN), titanium nitride (hereinafter referred to as TiN), and niobium nitride (hereinafter referred to as NbN), which is a nitride having a NaCl type crystal structure. It has been recognized that when annealing is performed under certain conditions, fine dispersion of Cu sulfide is suppressed and magnetic characteristics are remarkably improved. As a result of further detailed investigations on the form and structure of precipitates in steel, this phenomenon is especially avoided when Cu sulfide is precipitated together with NaCl-type nitride, and (A) Cu sulfide is not dispersed alone. And (B) Cu sulfide was found to have good lattice matching with the ground iron. Further, it has been found that composite precipitation of Cu sulfide and NaCl type nitride can occur when the lattice matching between NaCl type nitride and Cu sulfide, which are precipitation nuclei, is optimized.

This invention is made | formed based on the said knowledge, and makes the following (1)-(5) a summary.
(1) The non-oriented electrical steel sheet according to one aspect of the present invention has a chemical component of mass%,
C: 0.0001-0.01%, Si: 0.05-3.5%, Mn: 0.01-2.0%, Al: 0.002-2.0%, S: 0.0010 0.05%, P: 0.001 to 0.20%, N: 0.0005 to 0.02%, Cu: 0.01 to 3.00%, and V: 0.002 to 0 .20%, Nb: 0.002 to 0.20%, Ti: 0.002 to 0.10% of one or more, and the balance has a chemical composition of Fe and impurities. I _{2θ = 46.8} , which is the diffraction intensity of Cu sulfide having a hexagonal structure appearing at 2θ = 46.8 °, and a Cubic structure appearing at 2θ = 34.4 ° obtained in X-ray diffraction with respect to the extraction residue Cubic structure appearing at the diffraction intensity of VN, I _{2θ = 34.4} and 2θ = 43.3 ° I _{2θ = 43.3,} which is the diffraction intensity of TiN, and I _{2θ = 51.6} , which is the diffraction intensity of NbN having a Cubic structure that appears at 2θ = 51.6 °, satisfy the condition of the following formula 1.
0.1 ≦ I _{2θ = 46.8} / (I _{2θ = 34.4} + I _{2θ = 43.3} + I _{2θ = 51.6} ) Equation 1
(2) I _{2θ =} the diffraction intensity of Cu sulfide having a Cubic structure appearing at 2θ = 32.1 ° obtained in X-ray diffraction with respect to the electrolytic extraction residue of the non-oriented electrical steel sheet described in (1) above. _32.1 and I _{2θ = 46.8} , which is the diffraction intensity of Cu sulfide having a hexagonal structure that appears at 2θ = 46.8 °, satisfy the condition of the following equation (2).
I _{2θ = 32.1} / I _{2θ = 46.8} ≦ 3.0 ... Formula 2
(3) A method for producing a non-oriented electrical steel sheet according to the present invention includes:
A hot-rolling step of hot-rolling a steel piece having the chemical composition described in (1) above to obtain a hot-rolled steel plate, a pickling step of pickling the hot-rolled steel plate after the hot-rolling step, and the acid A cold rolling step of cold rolling the hot rolled steel plate after the washing step to obtain a cold rolled steel plate, and a finish annealing step of cooling the cold rolled steel plate after annealing,
In the finish annealing step, the temperature is T1 (° C.) or higher represented by the following formula 3 and T2 (° C.) to T4 (° C.) represented by the following formulas 3 to 5 at a temperature of T7 (° C.) or lower, which is the highest temperature. Hold for 3600 seconds,
In the subsequent cooling, the average cooling rate in the temperature range from T1 (° C.) or less shown in the following formula 3 to T5 (° C.) or more shown in the following formula 7 is set to 50 ° C./second or less.
T1 (° C.) = 15000 / (12-log ₁₀ ([% Cu] ² × [% S]))-273 Formula 3
T2 (° C.) = 10700 / (5-log ₁₀ ([% V] × [% N])) − 273
T3 (° C.) = 10200 / (4-log ₁₀ ([% Nb] × [% N])) − 273 (Formula 5)
T4 (° C.) = 16800 / (8-log ₁₀ ([% Ti] × [% N])) − 273 Formula 6
T5 (° C.) = 15000 / (12-log ₁₀ ([% Cu] ² × [% S]))-323 Formula 7
T6 (° C.) = 15000 / (12−log ₁₀ ([% Cu] ² × [% S]))-423 Formula 8
In the above formulas 3 to 8, [% Cu] is the content of Cu in mass%, [% S] is the content of S in mass%, and [% V] is the mass% of V. [% Nb] is the content of Nb in mass%, [% Ti] is the content of Ti in mass%, and [% N] is the content of N in mass%. Amount.
(4) The manufacturing method of the non-oriented electrical steel sheet according to (3) described above includes the highest temperature T7 (T2 (° C.) to T4 (° C.) higher than the T1 (° C.) in the finish annealing step. C.) for 10 to 3600 seconds, and in subsequent cooling, the average cooling rate in the temperature range from T1 (° C.) or lower to T5 (° C.) or higher is set to 50 ° C./second or lower. The average cooling rate in the temperature range from less than (° C.) to above T6 ° C. is set to exceed 50 ° C./second.
(5) The method for producing a non-oriented electrical steel sheet according to the above (3) or (4) is a hot-rolled sheet annealing process for annealing the hot-rolled steel sheet between the hot-rolling process and the pickling process. In the hot-rolled sheet annealing step, holding is performed for 10 to 3600 seconds at T7 ° C or higher, and in subsequent cooling, in the temperature range from T7 ° C or lower to T9 (° C) or higher in Formula 9 below. The average cooling rate is 50 ° C./second or less.
T9 (° C.) = T8 (° C.) − 150 (Equation 9)
However, T8 (° C.) in Equation 9 is the lowest temperature among the above T2 (° C.) to T4 (° C.).

According to the present invention, with respect to the non-oriented electrical steel sheet, it is possible to avoid single precipitation of fine Cu sulfide without performing purification, slab heating temperature reduction, optimization of hot rolling conditions, etc. A non-oriented electrical steel sheet excellent in iron loss can be provided by controlling the precipitation form to have a positive effect on iron loss.
In addition, according to this invention, the characteristics (magnetic flux density, workability, etc.) other than the iron loss calculated | required in a non-oriented electrical steel sheet can ensure equivalent or more than the conventional material.

  Hereinafter, a non-oriented electrical steel sheet according to an embodiment of the present invention (sometimes referred to as a non-oriented electrical steel sheet according to this embodiment) and a manufacturing method thereof will be described in detail. All% of content is mass%.

C: 0.0001 to 0.01%
C significantly deteriorates the iron loss by magnetic aging. Therefore, the upper limit of the C content is set to 0.01%. Since C mixes at least 0.0001% as a playing element, the lower limit of the C content is set to 0.0001%. From the viewpoint of improving the magnetic flux density, 0.0001% to 0.003% is preferable. More preferably, it is 0.0001% or more and 0.001% or less.

Si: 0.05 to 3.5%
The Si content is set to 0.05 to 3.5% from the viewpoint of securing iron loss and plate passing. If the Si content is less than 0.05%, good iron loss cannot be obtained. On the other hand, when the Si content exceeds 3.5%, SiN precipitates, and it becomes difficult to precipitate NaCl-type nitrides, and there is a possibility that the iron loss cannot be sufficiently improved. Si content becomes like this. Preferably it is 0.1-2.0%, More preferably, it is 0.3-1.0%.

Mn: 0.01 to 2.0%
Since Mn reacts with S to form a sulfide, it is an important element in the present invention. When Mn is present in the steel, MnS is precipitated, so that the amount of Cu ₂ S deposited decreases, and Cu ₂ S tends to precipitate finely. Therefore, the upper limit of the Mn content is set to 2.0%. On the other hand, if the Mn content is less than 0.01%, the steel plate becomes brittle during hot rolling. Therefore, the lower limit of the Mn content is 0.01%. Preferably, the Mn content is 0.05 to 1.0%, more preferably 0.10 to 0.50%.

Al: 0.002 to 2.0%
Molten steel with a high Al content deteriorates operability during casting and causes embrittlement of the steel sheet. Furthermore, Al forms AlN, lowering the precipitation temperature of VN, TiN, and Nb, which are precipitates utilized in the present invention, making it difficult to enjoy the effects of the invention. Therefore, the upper limit of the Al content is set to 2.0%. On the other hand, Al exists in the material as an inevitable playing card element. Therefore, the lower limit of the Al content is set to 0.002%. The Al content is preferably 0.01 to 1.2%, more preferably 0.1 to 0.8%.

P: 0.001 to 0.20%
P has the effect of increasing the hardness of the steel sheet and improving the punchability. A small amount of P has an effect of improving the magnetic flux density. In order to obtain these effects, the lower limit of the P content is 0.001%. P content is preferably 0.005 to 0.10%, more preferably 0.01 to 0.05%.

S: 0.0010 to 0.05%
The S content is directly related to the sulfide content. If the S content is excessive, S is present in the steel in a solid solution state, and the steel becomes brittle during hot rolling. Therefore, the upper limit of S content is 0.05%. On the other hand, if S is not present, Cu is finely deposited as metal Cu and causes iron loss deterioration. Therefore, the lower limit for the S content is 0.0010%. Preferably it is 0.0020-0.02%, More preferably, it is 0.0040-0.01%, More preferably, it is 0.0045-0.01%.

N: 0.0005 to 0.02%
Since N is an element that forms a nitride, it is one of the particularly important elements in the present invention. However, if the N content is excessive, the amount of deposited nitride increases too much, which hinders crystal grain growth and degrades the magnetic flux density. Therefore, the upper limit of N content is set to 0.02%. When N is small, it is difficult to enjoy the effects of the present invention, so the lower limit of the N content is 0.0005%. Preferably it is 0.0010 to 0.008%, More preferably, it is 0.0040 to 0.008%.

Cu: 0.01 to 3.00%
Since Cu forms Cu sulfide, it is a particularly important element in the present invention. When there is too much Cu content, since Cu sulfide exceeds the solid solution temperature of NaCl type nitride, application of the present invention becomes difficult. Therefore, the upper limit of Cu content is set to 3.00%. On the other hand, when there is too little Cu, other fine sulfides, such as TiS, precipitate and cause iron loss deterioration, so the lower limit of the Cu content needs to be 0.01%. Preferably it is 0.10 to 1.00%, More preferably, it is 0.20 to 0.50%.

  V, Nb, and Ti are important elements in the present invention for forming a nitride having a NaCl-type crystal structure, and it is necessary to contain one or more of them.

V: 0.002 to 0.20%
Since the V content is directly related to the VN precipitation amount, it is an important element in the present invention. Although there is no problem if a large amount of V exists, the upper limit of the V content is set to 0.20% from the viewpoint of manufacturing cost. On the other hand, V exists in the material as an inevitable playing card element. Therefore, the lower limit of the V content is set to 0.002%. Preferably it is 0.005-0.1%, More preferably, it is 0.01-0.05%.

Nb: 0.002 to 0.20%
Since the Nb content is directly related to the NbN amount, it is an important element in the present invention. If the Nb content is excessive, NbC is generated in addition to NbN, and solid solution C, which is effective in improving the magnetic flux density, is reduced. Therefore, the upper limit of Nb content is 0.20%. On the other hand, from the viewpoint of achieving both toughness and strength, the lower limit of the Nb content is set to 0.002%. Preferably it is 0.005-0.1%, More preferably, it is 0.01-0.05%.

Ti: 0.002-0.10%
Since the Ti content is directly related to the TiN precipitation amount, it is an important element in the present invention. If the Ti content is excessive, fine carbides are formed, grain growth is suppressed, and magnetic flux density is reduced. Therefore, the upper limit of Ti content is 0.10%. On the other hand, since Ti exists in the material as an inevitable playing card element, the lower limit is made 0.002%. Preferably it is 0.005-0.05%, More preferably, it is 0.010-0.025%.

  The non-oriented electrical steel sheet according to the present embodiment basically contains the above-described chemical components and the balance is made of Fe and impurities. However, Mo, W, In, etc. for the purpose of further improvement of magnetic properties, improvement of properties required for structural members such as strength, corrosion resistance and fatigue properties, improvement of castability and plate-through property, use of scrap, etc. Trace elements such as Sn, Bi, Sb, Ag, Te, Cr, Co, Ni, Se, Re, Os, Zr, Hf, Ta, Y, and La are contained in a total range of 0.5% or less. Also good. Moreover, even if these elements are mixed in a range of 0.5% or less in total, the effect of the present embodiment is not impaired.

  Next, the state of Cu sulfide, which is an important control factor in the non-oriented electrical steel sheet according to the present embodiment, will be described. It is difficult to completely eliminate the presence of Cu sulfide in the steel sheet. Therefore, in the non-directional electromagnetic according to the present embodiment, in addition to positively precipitating S as Cu sulfide, the Cu sulfide to be precipitated is controlled so as to be compositely precipitated using nitride as a precipitation nucleus. Get good iron loss.

  The ease of composite precipitation of Cu sulfide and nitride is determined by the crystal structure of nitride, which is the precipitation nucleus, that is, the periodicity of atomic arrangement. That is, when the nitride has a NaCl-type crystal structure, the nitride functions most effectively as a Cu sulfide precipitation nucleus. The nitride of the NaCl type crystal structure is, for example, VN, TiN, or NbN. The crystal system of Cu sulfide at the time of complex precipitation is Hexagonal, and the crystal structure can be identified by X-ray diffraction (XRD).

In the non-oriented electrical steel sheet according to the present embodiment, for example, when X-ray diffraction (XRD) is performed on the electrolytic extraction residue of the steel sheet, the diffraction intensity of VN having a Cubic structure appearing at 2θ = 34.4 °. Diffraction intensity of TiN having a Cubic structure appearing at certain I _{2θ = 34.4} and 2θ = 43.3 ° I _{2θ = 43.3} and diffraction of NbN having a Cubic structure appearing at 2θ = 51.6 ° The intensity I _{2θ = 51.6} and the diffraction intensity derived from Cu sulfide (Hexagonal) at 2θ = 46.8 ° ± 3 ° satisfy I _{2θ = 46.8} satisfying the following formula 1. Control. I _{2θ = 46.8} corresponds to the abundance of Cu sulfide (Hexagonal) co-precipitated with NaCl-type nitride, and (I _{2θ = 34.4} + I _{2θ = 43.3} + I _{2θ = 51.6} ) Corresponds to the abundance of NaCl-type nitrides, that is, precipitation nuclei. When the Cu sulfide (Hexagonal) is not present in a certain amount or more with respect to the precipitation nuclei, the effect of the present invention cannot be enjoyed, so the lower limit of the right side of the following formula 1 is set to 0.1. The upper limit of the right side of the following formula 1 is not particularly limited, but the upper limit is preferably 100 because the amount of Cu sulfide (Hexagonal) that can be combined with NaCl-type nitride is limited. Since there is an optimal balance between the abundance of the NaCl type nitride and the abundance of Cu sulfide, I _{2θ = 46.8} / (I _{2θ = 34.4} + I _{2θ = 43.3} + I _{2θ = 51.} The value of ₆ ) is more preferably 0.5 or more and 50 or less. A more preferable range is 3.0 or more and 10 or less.

0.1 ≦ I _{2θ = 46.8} / (I _{2θ = 34.4} + I _{2θ = 43.3} + I _{2θ = 51.6} )

Further, the present inventors have found that a Cubic structure (cubic structure) exists in addition to a hexagonal structure (close-packed hexagonal structure) in the structure of Cu sulfide in steel. Since Cu sulfide having a Cubic structure is difficult to be compounded with NaCl type nitride, in the non-oriented electrical steel sheet to which the present invention is applied, the Cu sulfide having the Cubic structure is compared with the Cu sulfide having the Hexagonal structure. It is preferable that the abundance is reduced. Therefore, it is the diffraction intensity of Cu sulfide having a Hexagonal structure appearing at _{2θ = 36.8,} and the diffraction intensity of Cu sulfide having a Cubic structure appearing at 2θ = 32.1 °. It is preferable that I _{2θ = 46.8} satisfies the condition of the following formula 2. Since the effect of the present invention can be enjoyed as the amount of Cu sulfide having a Cubic structure _decreases , the preferable range of I _{2θ = 46.8} / I _{2θ = 32.1} is 0 or more and 1.0 or less, and more preferably 0 or more and 0.00. 5 or less.

I _{2θ = 32.1} / I _{2θ = 46.8} ≦ 3.0 (Formula 2)

  In XRD, a diffraction peak is observed at a specific 2θ position according to the crystal structure of the sample. However, the crystal lattice of the precipitate in the steel material fluctuates due to various factors such as Fe solid solution with respect to the precipitate and lattice matching with the base iron matrix. Accordingly, the 2θ value at which diffraction appears includes at least ± 3 ° within an error range. The identification of the crystal structure may be verified using JCPDS-CARD, which is a database of crystal lattices. However, Cu sulfide (Hexagonal) is 23-0958, and Cu sulfide (Cubic) is JCPDS-CARD: 00-012-0174. , 00-024-0061, 023-0962, 053-0522, 33-0491, 33-0492, 070-9133, and the like, which fall within an error range of ± 3 ° of 2θ.

In particular, in Cu sulfide, by partially replacing Fe and S, Cu ₉ Fe ₉ S ₁₆ (JCPDS: 00-027-0165), Cu ₅ FeS ₄ (JCPDS: 024-0050, 089-2620) and CuFe ₂ S ₃ (JCPDS: 027-0166), CuFeS ₂ (JCPDS: 075-0253, 041-1404) and other precipitates are formed, and the crystal system of such Cu—Fe—S compounds is also Cubic. If a 200 diffraction peak is observed at 2θ = 32.1 ° ± 3 °, it can be defined as I _{2θ = 32.1} . In the above error range, when two or more diffraction peaks exist for Cu sulfide (Cubic), the sum of these peak intensities is I _{2θ = 32.1} .

  In general, the diffraction intensity of XRD is the height from the background of the spectrum to the peak. The XRD diffraction intensity (peak intensity) in the present embodiment can also be removed using the software described in Non-Patent Documents 3 and 4.

Next, the manufacturing method of the non-oriented electrical steel sheet according to this embodiment will be described.
The non-oriented electrical steel sheet according to this embodiment is melted in a converter in the same manner as a normal electrical steel sheet so as to have the above-described component composition, and continuously rolled into a steel piece that is hot-rolled, hot-rolled sheet annealed, It can be manufactured by performing cold rolling, finish annealing, or the like.

  The hot rolling is not particularly limited, and the iron loss improvement effect can be enjoyed regardless of the hot rolling method such as direct feed hot rolling or continuous hot rolling and the slab heating temperature. The cold rolling is not particularly limited, and the iron loss improvement effect can be enjoyed regardless of the cold rolling method such as cold rolling and warm rolling twice or more and the cold rolling reduction ratio. Further, in addition to these steps, an insulating film formation or a decarburization step may be performed. Moreover, there is no problem even if it is manufactured not by a normal process but by a process such as a thin slab or a continuous casting process in which the production of a ribbon by the rapid solidification method or the hot rolling process is omitted.

  However, when obtaining the non-oriented electrical steel sheet according to the present embodiment, it is important to pass through a thermal history as described below in the finish annealing step. That is, the entire amount of Cu sulfide is dissolved in the final annealing step, and control is performed so that Cu sulfide and NaCl-type nitrides VN, TiN, and NbN are combined and precipitated during cooling in the final annealing step.

  In the present invention, the following six temperatures T1 to T6 (° C.) are important. T1 (° C.) is the solid solution start temperature of Cu sulfide, and T2, T3, and T4 (° C.) are the solid solution start temperatures of VN, TiN, and NbN, respectively. T5 (° C.) is an upper limit temperature at which Cubic-type Cu sulfide is precipitated, and T6 (° C.) is a lower limit temperature at which Cubic-type Cu sulfide is precipitated.

T1 (° C.) = 15000 / (12-log ₁₀ ([% Cu] ² × [% S]))-273 Formula 3
T2 (° C.) = 10700 / (5-log ₁₀ ([% V] × [% N])) − 273
T3 (° C.) = 10200 / (4-log ₁₀ ([% Nb] × [% N])) − 273 (Formula 5)
T4 (° C.) = 16800 / (8-log ₁₀ ([% Ti] × [% N])) − 273 Formula 6
T5 (° C.) = 15000 / (12-log ₁₀ ([% Cu] ² × [% S]))-323 Formula 7
T6 (° C.) = 15000 / (12−log ₁₀ ([% Cu] ² × [% S]))-423 Formula 8

  In the above formulas 3 to 8, [% Cu] is the content of Cu in mass%, [% S] is the content of S in mass%, and [% V] is the mass% of V. [% Nb] is the content of Nb in mass%, [% Ti] is the content of Ti in mass%, and [% N] is the content of N in mass%. Amount.

  In the non-oriented electrical steel sheet according to the present embodiment, the effect of iron loss improvement is obtained by complex precipitation of Cu sulfide and NaCl type nitride. In general, Cu sulfide has a high precipitation rate, and even if it is solid-dissolved by finish annealing, it is finely re-deposited alone during the subsequent cooling, which adversely affects iron loss. However, if NaCl-type nitride is present at the start of cooling, Cu sulfide is complex-precipitated with NaCl-type nitride as a nucleus during cooling, so that fine precipitation can be suppressed. Moreover, when this composite precipitate (Cu sulfide + NaCl type nitride) is present, good iron loss can be obtained. For this reason, it is necessary to make NaCl type nitride exist at the time of the cooling start by controlling the holding temperature of the finish annealing to a temperature range in which NaCl type nitride is not dissolved while dissolving Cu sulfide.

  That is, in the finish annealing step, the Cu sulfide can be completely dissolved by holding the Cu sulfide at a solid solution temperature T1 (° C.) or higher for 10 seconds or longer. If the holding temperature is less than T1 (° C.), Cu sulfide cannot be dissolved. However, if the steel sheet exceeds the melting temperature of the NaCl type nitride, the NaCl type nitride, which is the precipitation nucleus of Cu sulfide, will disappear, and the effect of the present invention cannot be enjoyed. Therefore, the upper limit of the holding temperature needs to be T7 (° C.) which is the highest temperature among T2 to T4 (° C.).

  Further, the holding time (staying time of T1 (° C.) or more) is set to 10 seconds or more and 3600 seconds or less. If the holding time is less than 10 seconds, solid solution does not proceed sufficiently. On the other hand, when heated for more than 3600 seconds, other fine sulfides such as TiS having a slow deposition rate are generated, which adversely affects iron loss improvement. A preferable holding time is 100 seconds or more and 1000 seconds or less.

  In the finish annealing step, Cu sulfide (Hexagonal) is precipitated together with NaCl-type nitride to avoid fine precipitation of Cu sulfide. Control of the cooling rate in the temperature range below T1 (° C.) is also an important control factor in the present invention. If the cooling rate in the temperature range of T1 to T5 (° C.) is too large, Cu sulfide (Hexagonal) cannot be sufficiently precipitated, and NaCl type nitride and Cu sulfide do not precipitate together and enjoy the effects of the present invention. Can not. Therefore, the cooling rate in the temperature range of T1 to T5 (° C.) needs to be 50 ° C./second or less. On the other hand, the smaller the cooling rate, the greater the effect of the present invention. However, in actual production, natural air cooling is practical, and in this case, the lower limit of the cooling rate is 0.01 ° C./second. A preferable cooling rate is 0.01 ° C./second or more and 20 ° C./second or less.

  It is also important to shorten the residence time in the precipitation temperature region of Cu sulfide having a Cubic-type crystal structure that is difficult to be combined with NaCl-type nitride. Therefore, the average cooling rate in the temperature range from T6 ° C. to T5 ° C. is set to exceed 50 ° C./second. The greater the cooling rate in this temperature range, the higher the effect of the present invention. However, considering the influence of cooling strain introduced into the steel sheet, the preferred range is 75 ° C./second or more and 100 ° C./second or less. In addition, when switching a cooling rate from 50 degrees C / second or less to exceeding 50 degrees C / second, what is necessary is just to switch when the steel plate temperature becomes T5 (degreeC).

  There are many nitrides having various crystal structures in the hot-rolled sheet after the hot-rolling step. For this reason, in the step prior to the finish annealing, it is effective to further solidify the nitride in the plate once and re-deposit it again as a NaCl-type precipitate in order to further demonstrate the effects of the present invention. Therefore, the nitride (VN, NbN, TiN) in the hot-rolled sheet is completely dissolved at a temperature equal to or higher than T7 (° C.), and is reprecipitated as NaCl-type nitride during the subsequent cooling.

  The NaCl-type nitrides VN, NbN, and TiN have different solid solution temperatures, but the steel plate is held at a temperature equal to or higher than T7 (° C.), which is the highest of these solid solution temperatures, and then cooled. The effect of the present invention can be enjoyed by slowly cooling the process to precipitate a large amount of NaCl-type nitride. The upper limit of the temperature range for slow cooling is T7 (° C.) which is the steel sheet holding temperature, and the lower limit of the temperature range is T9 (° C.) described in the following formula 9. T8 (° C.) in Equation 9 is the lowest temperature among the solid solution temperatures T2 to T4 (° C.) of the NaCl type nitride. The reason for setting the lower limit of the temperature range for slow cooling to T9 (° C.) is to control the cooling rate even in the range of at least T8 to T9 ° C. in order to deposit precipitates having a solid solution temperature of T8 (° C.) during cooling. It is because it is necessary to perform. That is, in the present invention, in the hot-rolled sheet annealing step, the cooling rate in the temperature range from T9 (° C.) to T7 (° C.) is set to 50 ° C./second or less.

  T9 (° C.) = T8 (° C.) − 150 (Equation 9)

  The smaller the cooling rate in this temperature range, the greater the effect of the present invention. However, in actual production, natural air cooling is practical, and in this case, the lower limit of the cooling rate is 0.01 ° C./second. A preferable cooling rate at T9 to T7 ° C. is 0.01 ° C./second or more and 20 ° C./second or less.

  The holding time for hot-rolled sheet annealing (stay time of T1 (° C.) or more) is 10 seconds or more and 3600 seconds or less. If the holding time is less than 10 seconds, solid solution does not proceed sufficiently. On the other hand, when heated for more than 3600 seconds, other fine sulfides such as TiS having a slow deposition rate are generated, which adversely affects iron loss improvement. A preferable holding time is 100 seconds or more and 1000 seconds or less.

  Generally, the better the consistency between the precipitate and the steel interface, the smoother the domain wall movement and the better the iron loss. Cu sulfide precipitates alone and very finely (<5 nm), which adversely affects iron loss. However, in the non-oriented electrical steel sheet according to the present embodiment, Cu sulfide is combined with NaCl-type nitride. Thus, fine precipitation is avoided. In the non-oriented electrical steel sheet according to the present embodiment, it is considered that domain wall movement is easy and a good iron loss is exhibited.

The technical contents of the present invention will be further described below with reference to examples of the present invention. In addition, the conditions in the Example shown below are one example of conditions used in order to confirm the feasibility and effect of this invention, and this invention is not limited to this one example of conditions. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.
In addition, the underline in the table | surface used by the following description shows that it is outside the scope of the present invention.

<Example 1>
The ingots having the components shown in Table 1A and Table 1B are melted in vacuum, the ingot is heated at 1150 ° C., the hot rolling finish temperature is 850 ° C., the coiling temperature is 600 ° C., and the thickness is 2.0 mm. A rolled steel sheet was used. Thereafter, it was pickled and cold-rolled at a rolling reduction of 75% to obtain a cold-rolled steel sheet having a thickness of 0.50 mm. Subsequently, finish annealing was performed. The holding temperature of finish annealing was set to the range of T1 ° C. or higher and T7 ° C. or lower shown in Table 2 for each steel, and the holding time was 120 seconds. In the cooling process after finish annealing, the cooling rate between T1 and T5 (° C.) was set to 15 ° C./second. Table 2 shows the results of X-ray diffraction and magnetic characteristics (magnetic flux density and iron loss). In the table, “I _CuS / I _M ” indicates I _{2θ = 46.8} / (I _{2θ = 34.4} + I _{2θ = 43.3} + I _{2θ = 51.6} ).

  According to the iron loss, VG: very excellent, G: excellent, F: effect is seen, B: evaluated as a conventional level. The magnetic properties were evaluated according to JIS C 2550: 2000. Straightening annealing is not performed. For iron loss, W15 / 50 (W / kg) was evaluated. W15 / 50 is the iron loss when the frequency is 50 Hz and the maximum magnetic flux density is 1.5T. The magnetic flux density was evaluated using B50. B50 indicates the magnetic flux density at a magnetic field strength of 5000 A / m. In addition, the minimum target value of B50 was set to 1.50 T which is equivalent to the conventional material. The iron loss evaluation criteria for the samples were as follows.

VG (VeryGood): W15 / 50 (W / kg) <2.20
G (Good): 2.20 ≦ W15 / 50 (W / kg) ≦ 2.50
F (Fair): 2.50 <W15 / 50 (W / kg) ≦ 4.50
B (Bad): 4.50 <W15 / 50 (W / kg)

  For X-ray diffraction, a sample in which only inclusions were collected by a filter by a general extraction residue method described in Non-Patent Documents 4 and 5 was used as an analysis sample. XRD measurement was performed by wide-angle X-ray diffraction using CuKα rays described in Non-Patent Documents 4 to 6 as a probe.

As shown in Table _2, 0.1 or more invention steel _I CuS / _{I M,} compared with the comparative steel _I CuS / _{I M} is less than 0.1, it can be seen that the iron loss is improved.

<Example 2>
Ingots having the components shown in Table 1A were melted in vacuum, the ingot was heated at 1150 ° C., hot rolled at a finishing temperature of 875 ° C. and a coiling temperature of 630 ° C., and a hot rolled steel sheet having a thickness of 2.0 mm, did. Thereafter, it was pickled and cold-rolled at a rolling reduction of 75% to obtain a cold-rolled steel sheet having a thickness of 0.50 mm. Subsequently, finish annealing was performed for 120 seconds at a holding temperature in the range of T1 (° C.) to T7 (° C.) shown in Table 3. In the furnace cooling process after finish annealing, the cooling rate between T5 and T6 (° C.) was controlled at 75 ° C./second, and the cooling rate between T1 and T (5) ° C. was controlled at 15 ° C./second.

Table 3 also shows evaluation results of X-ray diffraction results and magnetic characteristics (magnetic flux density and iron loss). For the measurement of X-ray diffraction and magnetic properties, the same evaluation as in <Example 1> was performed. In Table 3, “I _cub / I _hex ” indicates I _{2θ = 32.1} / I _{2θ = 46.8} . No. In _{(c1.about.c4),} but _I CuS / _{I M} is is controlled in the scope the present _invention, are over _I cub _/ I _hex is 3.0, since the Cu sulfide Cubic structure was much precipitation, No. Compared with C1 to C6, the iron loss was slightly reduced, but the damage was improved as compared with the comparative steel in Table 1.

<Example 3>
Steel No. shown in Table 1A. The ingot having the component A1 was heated at 1150 ° C. and hot-rolled so that the hot rolling finishing temperature was 850 ° C. and the coiling temperature was 630 ° C. to obtain a hot-rolled sheet having a thickness of 2.0 mm. Thereafter, it was pickled and cold-rolled at a reduction rate of 75% to obtain a cold-rolled steel sheet having a thickness of 0.50 mm, and finish annealing was performed under the conditions shown in Table 4. Table 4 also shows the X-ray diffraction results, the precipitation state of the precipitates, and the evaluation results of the magnetic properties (magnetic flux density and iron loss). Evaluation similar to Example 1 was performed about the measurement of the X-ray diffraction, the magnetic characteristic, and the measurement of the precipitate.

No. in which the conditions for finish annealing are outside the scope of the present invention. d1~d6 _Both, small _I CuS / _{I M,} i.e. in order although NaCl-type precipitates were not successfully precipitated iron loss had deteriorated. No. D1 to D9 are finish annealing cooling steps, the cooling rate in the temperature range of T5 to T6 (° C.) is outside the scope of the present invention, but the cooling rate in the temperature range of T1 to T5 ° C. is within the scope of the present invention. The iron loss is no. It was superior to d1-d6. No. D10 and D11 exhibited particularly good iron loss because both the cooling rate in the temperature range of T1 to T5 ° C and the cooling rate in the temperature range of T5 to T6 ° C were within the invention range.

<Example 4>
Steel No. shown in Table 1A. The ingot having the component A1 was heated at 1100 ° C. and hot-rolled so that the hot-rolling finishing temperature was 850 ° C. and the winding temperature was 630 ° C. to obtain a hot-rolled plate having a thickness of 2.0 mm. This hot-rolled sheet was subjected to hot-rolled sheet annealing under the conditions shown in Table 5. Thereafter, it was pickled and cold-rolled at a rolling reduction of 75% to obtain a cold-rolled steel sheet having a thickness of 0.50 mm, and finish annealing was performed under the conditions shown in Table 5.

  Table 5 also shows evaluation results of X-ray diffraction results and magnetic characteristics (magnetic flux density and iron loss). For the measurement of X-ray diffraction and magnetic properties, the same evaluation as in <Example 1> was performed.

No. For any of the samples E1 to E6, the effect of the present invention was obtained because the temperature, time and cooling rate of finish annealing are within the scope of the present invention. In particular, the cooling rate between T7 and T9 ° C. of hot-rolled sheet annealing was controlled within a preferable range. In E5 and _E6, which is controlled in the preferred range _I CuS / _{I M,} was particularly good.

Claims (5)

Chemical composition is mass%,
C: 0.0001-0.01%, Si: 0.05-3.5%, Mn: 0.01-2.0%, Al: 0.002-2.0%, S: 0.0010 0.05%, P: 0.001 to 0.20%, N: 0.0005 to 0.02%, Cu: 0.01 to 3.00%, and V: 0.002 to 0 .20%, Nb: 0.002 to 0.20%, Ti: 0.002 to 0.10%, or a chemical composition comprising the balance of Fe and impurities.
I _{2θ = 46.8} , which is the diffraction intensity of Cu sulfide having a hexagonal structure appearing at 2θ = 46.8 °, and a Cubic structure appearing at 2θ = 34.4 ° obtained in X-ray diffraction with respect to the electrolytic extraction residue. I _{2θ = 34.4,} which is the diffraction intensity of VN, and I _{2θ = 43.3} , which is the diffraction intensity of TiN having a Cubic structure appearing at 2θ = 43.3 °, and Cubic, appearing at 2θ = 51.6 °. A non-oriented electrical steel sheet excellent in iron loss, wherein I _{2θ = 51.6} , which is the diffraction intensity of NbN having a structure, satisfies the condition of the following formula 1.
0.1 ≦ I _{2θ = 46.8} / (I _{2θ = 34.4} + I _{2θ = 43.3} + I _{2θ = 51.6} ) I _{2θ = 32.1} which is the diffraction intensity of Cu sulfide having a Cubic structure appearing at 2θ = 32.1 ° obtained by X-ray diffraction with respect to the electrolytic extraction residue, and a Hexagonal structure appearing at 2θ = 46.8 ° The non-oriented electrical steel sheet excellent in iron loss according to claim 1, wherein I _{2θ = 46.8} , which is the diffraction intensity of the Cu sulfide, satisfies the condition of the following formula (2).
I _{2θ = 32.1} / I _{2θ = 46.8} ≦ 3.0 (Formula 2) A hot-rolling step of hot-rolling a steel slab having the chemical composition according to claim 1 to obtain a hot-rolled steel plate, a pickling step of pickling the hot-rolled steel plate after the hot-rolling step, and the pickling A cold rolling step of cold rolling the hot rolled steel sheet after the process to obtain a cold rolled steel sheet, and a finish annealing step of cooling the cold rolled steel sheet after annealing,
In the finish annealing step, the temperature is T1 (° C.) or higher represented by the following formula 3 and T2 (° C.) to T4 (° C.) represented by the following formulas 3 to 5 at a temperature of T7 (° C.) or lower, which is the highest temperature. Hold for 3600 seconds,
In the subsequent cooling, the iron loss is characterized in that the average cooling rate in the temperature range from T1 (° C.) or less shown in the following formula 3 to T5 (° C.) or more shown in the following formula 7 is 50 ° C./sec or less. Method of non-oriented electrical steel sheet with excellent resistance.
T1 (° C.) = 15000 / (12-log ₁₀ ([% Cu] ² × [% S]))-273 Formula 3
T2 (° C.) = 10700 / (5-log ₁₀ ([% V] × [% N])) − 273
T3 (° C.) = 10200 / (4-log ₁₀ ([% Nb] × [% N])) − 273 (Formula 5)
T4 (° C.) = 16800 / (8-log ₁₀ ([% Ti] × [% N])) − 273 Formula 6
T5 (° C.) = 15000 / (12-log ₁₀ ([% Cu] ² × [% S]))-323 Formula 7
T6 (° C.) = 15000 / (12−log ₁₀ ([% Cu] ² × [% S]))-423 Formula 8
In the above formulas 3 to 8, [% Cu] is the content of Cu in mass%, [% S] is the content of S in mass%, and [% V] is the mass% of V. [% Nb] is the content of Nb in mass%, [% Ti] is the content of Ti in mass%, and [% N] is the content of N in mass%. Amount. In the finish annealing step, holding is performed for 10 to 3600 seconds at T1 (° C.) or higher and T2 (° C.) to T4 (° C.) below the highest temperature T7 (° C.).
In the subsequent cooling, the average cooling rate in the temperature range from T1 (° C.) or lower to T5 (° C.) or higher is set to 50 ° C./second or lower, and in the temperature range from less than T5 (° C.) to T6 ° C. or higher. The method for producing a non-oriented electrical steel sheet excellent in iron loss according to claim 3, wherein the average cooling rate is more than 50 ° C / second. Between the hot-rolling step and the pickling step, a hot-rolled sheet annealing step for annealing the hot-rolled steel plate,
In the hot-rolled sheet annealing step, holding for 10 to 3600 seconds at T7 ° C or higher,
5. The subsequent cooling is characterized in that the average cooling rate in the temperature range from the T7 ° C. or lower to the T9 (° C.) or higher in the following formula 9 is 50 ° C./second or lower. Of non-oriented electrical steel sheet with excellent iron loss.
T9 (° C.) = T8 (° C.) − 150 (Equation 9)
However, T8 (° C.) in Equation 9 is the lowest temperature among the above T2 (° C.) to T4 (° C.).